Spark plug



June 14', 1938. FlGARD 2,120,890

SPARK PLUG Filed Jan. 15, 1937 Patented June 14, 1938 PATENT OFFICE SPARK PLUG Pierre Figard, Paris, France Application January 15, 1937, Serial No.120fl29 In Lnxemburg January 2'1, 1936 2 Claims.

This invention relates to an improved spark plug which, for a substantially equal cost price, operates during a longer period bi time than the spark plugs constructed up to now. It has already beensuggested to provide spark plugs having, at each of their ends, electrodes capable of being inverted and successively put in service, the body of these spark plugs being constituted by two metal half-shells connected together by a member of insulating material, so that the halt-shell carrying the side electrode which is not in service is not earthed. A cap oi insulating material is fitted at the end of the spark plug the electrodes 01' which are not in service; this cap is provided with a terminal coming in contact with a central electrode, this allowing current to pass to the central electrode in service. 1

This arrangement allows of avoiding the production of sparks between the electrodes which are not in.service, but it is very dimcult to carry it out, as it is practically impossible to make the insulatingmember connecting both shells in such a manner that it has a 'sumcient mechanical resistance. v

This arrangement has another inconvenience in that said insulating member must have a relatively great length ior avoiding the production of sparks between the portion of the shell carrying the electrodes not in service and which is electrically connected to the central electrode, and the other portion oi the shell or the engine body, this necessitating the manufacture oi spark plugs of excessive length.

According to the invention, the insulating cap. covering the electrodes not in service, is provided with a tubular extension which covers and thus insulates the central electrode not in service from the shell 01' the spark plug and irom the side electrode spaced irom'the central electrode.

In practice before utilizing the spark plug, the electrodes carried by its shell are spaced away from the electrodes carried by the insulating body. For putting the spark plug in service, the

electrode of one of the ends of the shell must be curved and placed at the usual distance (4 to 5 tenths a millimeter ior instance) irom the corresponding electrode .0! the insulating body, then the plug is screwed in the cylinder head of the engine at this end of the shell. The insulating cap is secured to the other end oi the shelland it insulates the, electrode, provided at this end of said shell, irom the corresponding electrode of the insulating body which is in contact with-*the terminal or said insulating cap.

When the electrodes in service are worn, it sufllces to unscrew the plug and to use the electrodes oi the opposite end oi said plug alter having suitably curved the electrode carried by this end of the shell for placing it at the usual distance from the corresponding electrode carried by the insulating body. The insulating cap is then secured to the end of the plug carrying the worn electrodes after the side electrode of this end has been straightened or removed.

Moreover, according to the invention, the insulating body having two electrodes at each of its ends is arranged in a portion of a shell having two symmetrical screw threaded parts which can be screwed in another part of the same shell ll screwing in the cylinder head of the engine and having at least one side electrode; an insulating cap, covering the central electrode not in service, insulates the latter and allows the supply of electric current owing to, a terminal provided for N that purpose on said insulating-cap.

Two spark plugs made according to the invention are described hereinafter and illustrated in the accompanying drawing:

Fig. l is an axial longitudinal sectional view of a first spark plug.

Fig. 2 is an external view of the spark plug.

Fig. 3 is a sectional view made according to line A-A 0! F18. l.

Fig. 4 is an axial longitudinal sectional view of a second spark plug.

The plug illustrated in Figs. 1 to 3 of the accompanying drawing is constituted by a central body I, of insulating material, steatite for instance, ofgeneral biconical shape. .This body I' is provided, according to its longitudinal axis and embedded in its mass, with a metal rod 2 projecting beyond the ends 01' the body i for forming two electrodes 3- and 3 and in its middle portion is formed a circular groove 4 adapted to facilitate its cooling.

The insulating body I is arranged in a metal shell formed of a member 5* screwed in a member 5'', these two members 5- and 5 rigidly embracing the body I by taking a bearing on circular shoulders 8" and 6 of the latter, through the medium of metalloplastic packings I. v

The member 5" is externally provided with a portion I having a hexagonal cross section and the walls of which are perforated with holes I allowing aeration oi the inner empty space ll 01- the spark plug and, consequently, suitable cooling or the latter.

Both members 5 and 5" are each provided, on

the -one hand, with a screw threaded portion ls impossiblefor them to unscrew.

The spark plug such as above described has therefore, as shown in Figs. 1 and 2 of the draw ing, two substantially symmetrical ends each provided with a central electrode 3 -3 and with a side electrode l2i2 each group of electrodes S -IZ and 3 l2 can therefore be successively used according as the plug is screwed in the cylinder head at its screw threaded por tion II or il Before putting in service one of the two groups of electrodes, it is necessary to curve the side electrode fir -I2 for moving its end to a small distance (Q- to 5 tenths of a millimeter) from the central electrode 39-3.

The spark plug further comprises a cap id, of insulating material, which can be secured at one of its ends, for instance by being screwed on one of the portions li -l l This cap i3 is provided with a circular groove i3 adapted to receive the side electrode l2-l2 corresponding to the portion. H -l l on which. it is screwedfand with a terminal M the stem iii of which constitutes, within said cap it, a slotted socket l6 which covers the central electrode 3- 3. An annular extension ll of said cap i3 is interposed, when the latter is placed in position on the shell of the plug, between the socket it cover-- ing the central electrode and the portion llli of the shell.

This annular extension ll electrically insulates the central electrode, on the one hand, from the corresponding side electrode and, on the other hand, from the shell.

The terminal I4 is connected, as usual, to one of the terminals of the source of electric energy, the other terminal of which is earthed.

When one group of electrodes S -i12 or 3 E2 no longer ensures suitable ignition owing to wear, it sufilces to put the other group of elec trodes in service after having curved the corresponding side electrode. For securing the insulating cap I3 on the other end of the plug, it Stil fices to straighten or remove the other side elec trode.

The spark plug illustrated in Fig. 4 of the accompanying drawing is constituted by a central body i, made of insulating material, of general biconical shape and in the mass of which is embedded a rod 2 both ends of which project outside the body l andiform two electrodes 3 -9.,

The insulating body I is arranged in a portion l8 of a metal shell. 'Thisportion I8 is formed oi two members connected together by beading a ring l9, said members being each provided with a screw threaded portion 20 allowingthem to be screwed in another portion 2! of the same shell.

This portion 2| is screwed in the cylinder head of the engine and is provided with an electrode 22 which is placed at the usual distance from the 2,1ao,seo

electrode 3'-l" in service when the portion I8 is screwed on the portion Zl.

A cap 23, made of insulating material, is screwed on the screw threaded portion 20 and thus coversthe electrode 8-3 which is not in service. Said cap is perforated with a hole 24 for the passageof a clip 25 fitting on said electrode 3'3 not in use and allowing the passage or electric current to the other central electrode through a conductor 26.

I Preferably, the electrode 22 carried by the portion H is secured within the latter and in such a manner as to be directed tangentially to the electrode 3'--3 of the body 6 corresponding thereto.

When one of the electrodes 3 4 is worn or damaged, it sufilces to invert the body I with the portion I! of the shell for allowing the other electrode 3I to be used.

What I claim as my invention and desire to secure by Letters Patent ls:-

l. A spark plug comprising in combination, a substantially biconical shaped body formed of insulating material, an electrical conductor sealed in the longitudinal axis of said body and extend ing a relatively short distance beyond each. end of said body to provide a central electrode, a shell embracing said body and rigidly engaging the mid portion thereof, each end of said shell having a side electrode and a threaded portion so that either end of the shell may be threaded into the cylinder head of an internal combustion engine,

a removable cap formed of insulating material having internal threads for engaging the threads of the end or the shell opposite from the end "which is then intended to be inserted in the cylinder head, and an annular extension carried by said cap extending between said shell and'the end of said body to insulate the end of the central electrode irom said shell, and electrical conductive means carried by said cap for engaging the central electrode within said cap.

2. A spark plug comprising in combination, a substantially biconical shaped body formed of insulating material, an electrical conductor sealed in the longitudinal axis of said body and extending a relatively short distance beyond each end,

or said body to provide a central electrode, a shell embracing said body and rigidly engaging the mid portion thereof, each end of said shell having a side electrode and a threaded portion so that either end 01' the shell may be threaded into the cylinder head 01' an internal combustion engine, a removable cap formed of insulating material having internal threads for engaging the threads of the end-of the shell opposite from the end which is then intended to be inserted in the cylinder head, an annular extension having a conical shaped end carried by said cap, the end of said annular extension extending into wedging engagement between said shell and the end of said body to insulate the end of the central electrode from said shell and to'provide a support for the upper end ofsaid body and central electrode, and electrical conductive means carried by said cap for engaging the central electrode within the cap.

PIERRE FIGARD. 

